It has become recognized in recent years that the electronic and optical properties of metals and semiconductors change dramatically as the particulates of the materials are reduced to approach the nanometer size range of dimensions. At such size levels, the physical dimensions of the material may have a critical effect on the electronic or optical behaviour of the material. The restriction of the electronic wave function to smaller and smaller regions of space within a particle of material (the resonance cavity) is referred to as "quantum confinement". Semiconductor structures in the nanometer size range, exhibiting the characteristics of quantum confinement, are commonly referred to as "quantum dots" when the confinement is in three dimensions, "quantum wires" when the confinement is in two dimensions, and "quantum wells" when the confinement is in one dimension.
By the term "nanometer size range" as it is used herein, there is meant a size range from about 1-500 nanometers.
Such quantum dots, wires or wells can be fabricated with electrical contact between individual ones of them, so that semiconductor devices such as diodes, transistors, photodetectors and light emitting devices can be made from them. There is the potential for sharp transitions between tunnelling and non-tunnelling (on and off) states in devices fabricated from quantum dots and quantum wires, so that quantum dot and quantum wire devices could be the building blocks for digital nano electronics, an integrated circuit technology which will permit downscaling to be carried beyond what is currently achievable.
In reality, the quantum dot or quantum wire device consists of a collection of particles each having a resonance cavity so small that quantum confinement effects are very pronounced. For the device to be effective, therefore, there must be a very high degree of size uniformity of the particles making up the quantum dot or quantum wire device, so that each has substantially identical electronic and optical properties.